The present invention relates generally to impact printers or the like, and in particular to a failure detection circuit for an impact printer or the like having a plurality of hammer drive electromagnets and a plurality of switching transistors for respectively energizing the electromagnets in response to control signals for detecting a failure in each transistor and the associated electromagnet.
A failure detection circuit for detecting a failure in a hammer drive circuit of an impact printer is disclosed in Japanese Utility Model No. 52-3963. The disclosed detection circuit provides a check for the conduction or nonconduction of each power switching transistor and an open-circuit, or disconnection of the associated hammer drive electromagnet by comparing the logic level of a control signal for each transistor with the logic level of its output during normal operating condition of the impact printer. However, this control signal has a duration sufficient to drive the associated hammer drive electromagnet, the checking is not possible before the printer is put into operation, thus resulting in a waste of print paper.